Modern wireless communication systems may operate according to Institute of Electrical and Electronics Engineers (IEEE) standards such as the 802.16 standards for Wireless Metropolitan Area Networks (WMANs) including the IEEE 802.16e Draft Amendment to IEEE Standard for Local and Metropolitan Area Networks—Part 16: Air Interface for Fixed Broadband Wireless Access Systems—Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands.
According to IEEE 802.16e; each frame shall start with a downlink (DL) preamble. The DL preamble is transmitted in one of three defined subcarrier sets, each subcarrier set utilizing every third subcarrier starting from some predetermined number. The subcarriers used for DL preamble are binary phase shift keying (BPSK) modulated by one from 114 codewords defined for each sector and cell.
The frequency domain (FD) structure of the DL preamble provides a periodic (3 subsymbols) structure of continuous time waveform of DL preamble in time domain (TD). Because existing fast Fourier transform (FFT) sizes are not divisible by three, it is impossible to create a sequence of samples (of length equals power of two) having three identical TD subsymbols. In other words, conventional receiver (RX) sampling (with 2n samples per DL preamble) destroys the periodic structure sequence of DL preamble samples. A periodicity of the sampled DL preamble leads to increasing the complexity of synchronization schemes.